An acidic lumen pH in the epididymis and vas deferens is crucial for sperm maturation and storage. Impairment of the acidification capacity might, therefore, result in lower fertility. The aim of this proposal is to develop a thorough understanding of the factors responsible for the regulation of acidification in the epididymis and vas deferens. The proposed studies are divided into three specific aims addressing hormonal regulation under physiological conditions, as well as pathophysiological effects of environmental toxins such as heavy metals and xenoestrogens on acidification in the male reproductive tract, by looking at the impact of these factors on the function of the vacuolar H+ATPase (PP). Our hypothesis is that the PP is regulated by various factors, having short term and long term effects. Acute and chronic regulation of net H+ secretion by aldosterone, testosterone, estrogen, and angiotensin II, will be examined. The effects of heavy metals such as cadmium, lead and mercury will also be examined. The proposed studies will use a novel and highly accessible model of epithelial acidification and a multidisciplinary approach (cell biology, immunocytochernistry, H+-selective microelectrodes), to identify and dissect the pathway of proton secretion and its regulation. These studies will provide important information related to the poorly understood process of male reproductive tract acidification, transepithelial H+ transport in general, and the effects of environmental toxins on male reproductive capacity.